The overall goal of our proposed research is to develop and validate, using hypothesis-based research, an integrated, 6- degree of freedom, three-axis array of motion sensors and related software algorithms for use in prostheses that improve the balance of vestibular deficient individuals. The Research Project Grant (R01) is used instead of the Phased Innovation Award due to NIDCD funding constraints and because of our existing preliminary results. This proposal builds upon the results of a one-axis motion sensing device that uses tactile vibrators to display body tilt and that has been used to improve the balance in vestibular deficient subjects. Members of the proposed research team developed this limited-production device and the initial test protocols that validate it. Using existing partnerships with industry, commercially available miniature rate gyroscopes and linear accelerometers will be selected, tested, and assembled into a motion-sensing array. A set of algorithms specific to the selected hardware will be written to yield physiologically useful measurements. As part of the development process other members of the research community will be polled for their inputs. This technology will be validated by integrating it into a wearable prototype balance aid that uses estimates of body tilt to help subjects improve their balance. This application was selected because there is not presently a practical way of providing direct electric stimulation to the human vestibular nerve using implantable devices. The prototype balance aid will then be used by four investigators in two sites (Boston MA, and Portland OR) for hypothesis-based experiments about balance during standing and locomotion. This approach achieves the simultaneous goals of sensor development (consistent with the RFA), of validation by hypothesis-based research (consistent with the Research Project Grant mechanism mandated by NIDCD) and is a necessary step in the development of a prosthesis that improves the balance in vestibular deficient subjects.